As pipelines and flowlines age, it is inevitable that they will suffer from corrosion damage resulting in leaks. One approach to remedy this problem is to replace the pipeline or flowline, which is costly. Another procedure is to use pull-through polyethylene liners. In this procedure, the liner which has a diameter slightly larger than the internal diameter of the pipeline is pulled through a series of hydraulically powered rollers to reduce the diameter of the liner to something less than that of the metal pipeline. The reduced diameter liner is installed in the pipeline after which tension is released and the liner is allowed to return to its original size, restrained only by the steel pipeline. Because of strength limitations of the liner, it may only be installed in sections up to about 5,000 feet in length depending on the size of the pipe, the severity of twists and bends imposed on the liner during installation and the interior conditions of the pipe.
It is also known to provide a loose fitting plastic liner to extend the life of an existing pipeline. However, such plastic liners are not used in high pressure pipelines since with this procedure an existing pipeline is used simply as a "guide" to receive the loose fitting plastic insert. The loose fitting insert once installed in the pipeline serves as a new "pipeline"; the insert conveys the material formerly conveyed by the pipeline but in so doing must be capable of withstanding whatever pressures may be required to transport material therethrough. Such loose fitting plastic inserts are unsuitable for use in high pressure pipelines because they are not capable of withstanding the stress encountered when the interior region of the liner is pressurized forcing the liner to expand radially toward the internal walls of the pipeline.
In still another procedure, an expandable tubular plastic liner such as a polyethylene liner having an outside diameter less than the inside diameter of a pipeline is pulled into a pipeline. Subsequently, the liner is subjected to heated and pressurized fluids so as to emplace it firmly against the interior of the pipe.
It would be desirable to provide an improved process for the installation of plastic liners in pipelines or flowlines where a continuous pull-through procedure may be used.